Three aspects of the synthesis of fatty acids in mammalian tissues will receive special attention: 1. The formation of butyrate in liver cytosol. Formation of butyrate by the lactating mammary gland of herbivores is well known but its formation by other tissues has been missed so far. We have observed that 24-40% of the total number of moles of fatty acids formed in rat liver is butyric acid. 2. The role of a log chain fatty acid-binding protein, recently discovered is so far unclear. Investigations are to be undertaken to ascertain whether they have a role in the removal of the products formed, which are inhibitory to the enzyme and/or they are required to transport fatty acids from the site of their formation to the sites of lipid synthesis. 3. The studies on the role of beta-reductive formation of crotonyl-CoA, reported from this laboratory, will be extended to evaluate its significance.